Many herbicides injure crop plants at herbicide application rates necessary to control weed growth. Accordingly, many herbicides cannot be used for controlling weeds in the presence of certain crops. Uncontrolled weed growth, however, results in lower crop yield and reduced crop quality inasmuch as weeds compete with crops for light, water and soil nutrients. Reduction of herbicidal injury to crops without an unacceptable corresponding reduction of herbicidal action on the weeds can be accomplished by use of crop protectants known as herbicide "antidotes" or "safeners".
There are several classes of 2,4,5-substituted-thiazoles known as antidotes for herbicides. U.S. Pat. No. 4,199,506 and No. 4,437,876 to Howe et al describe 2-halo-4-substituted-5-thiazolecarboxylic acids and derivatives as antidotes for protecting corn, rice and sorghum from thiocarbamate herbicides such as triallate, or acetamide herbicides such as alachlor and acetochlor. U.S. Pat. No. 4,284,426 to Howe et al describes 2-chloro-4-substituted-5-thiazolemethyl substituted compounds as antidotes for protecting sorghum treated with triallate, alachlor, butachlor or propachlor herbicides. U.S. Pat. No. 4,303,439 to Howe et al describes 2-substituted-4-substituted-5-oxazolecarboxylic acids/esters as antidotes for protecting rice, sorghum or wheat from triallate, alachlor or butachlor herbicides. The 2-position of the thiazole ring is substituted by hydrido, alkoxy, halo or phenoxy groups. U.S. Pat. No. 4,308,391 to Howe et al describes 2-amino-4-substituted-5-thiazolecarboxylic acids and derivatives as intermediates to preparation of 2,4,5-substituted-thiazoles antidote compounds such as shown in aformentioned U.S. Pat. No. 4,199,506, No. 4,284,426 and No. 4,437,876.
Other classes of 2-aminothiazoles are known having various utilities. For example, U.S. Pat. No. 3,505,055 to von Schmeling describes 2-amino-4-methyl-5-carboxamido-thiazole compounds as plant growth regulants and as fungicides for coating and protecting crop seed. The 2-amino moiety is mentioned as substitutable by alkyl or phenyl groups. U.S. Pat. No. 3,542,801 to Manning describes 2-amino-4-(2-aminoethylamino)-5-halophenyl-thiazole compounds useful as hypotensive agents. There is no substitution shown for the 2-amino moiety. U.S. Pat. No. 3,547,917 to Kulka et al describes 2-amino-4-methylthiazole-5-carboxamides as fungicides and plant growth regulants. The 2-amino and 5-carboxamide moieties are mentioned as substitutable with many classes of radicals including alkyl, haloalkyl, cycloalkyl, alkenyl, phenyl, halophenyl and alkylphenyl. The Kulka et al '917 patent also mentions that N-heterocyclic groups may be substituted on the 2-amino nitrogen atom, such as furfuryl, .alpha.-pyridyl, or benzothiazolyl groups, and that the 2-amino nitrogen atom itself may be part of a heterocyclic ring such as a morpholido group. U.S. Pat. No. 3,879,531 to Ariyan et al describes 2-amino-4-methyl-5-thiazolecarboxamides for use as psychotherapeutic agents. The 2-amino moiety is shown as substitutable with methyl, ethyl or nitroso groups. The carboxamide nitrogen is shown as substitutable with hydrido, alkyl, phenyl or aralkyl groups. U.S. Pat. No. 3,933,838 to Manghisi et al describes 2-amino-4-aryl-5-substituted-thiazole compounds having various pharmacological properties, e.g., as antibacterial, anti-inflammatory, anti-ulcer or antipyretic agents. The 2-amino moiety is mentioned as substitutable with alkyl, cycloalkyl, phenyl, halophenyl, alkylphenyl, alkoxyphenyl or aralkyl. The thiazole 5-position substituents of Manghisi '838 comprise a large class, all members of which are characterized in being attached to the thiazole 5-position carbon through one, two or three methylene groups.
Weed control for corn and sorghum crops is one of the oldest and most highly developed areas in weed science. Thus, for a herbicide product to be accepted commercially, such herbicide product must provide a relatively high level of control of both grassy and broadleaf weeds in corn and sorghum, in addition to meeting several other criteria. For example, the herbicide must possess relatively high unit activity so that lower rates of herbicide application are feasible. Lower application rates are desirable in order to minimize exposure of the environment to the herbicide. At the same time, such herbicide must be selective in herbicidal effect so as not to injure the crops. Herbicidal selectivity can be enhanced by use of an appropriate antidote in combination with the herbicide. But identification of an antidote having high safening activity suitable for a commercially-effective herbicide is a highly complicated task. Whether a compound or class of compounds provides efficacious antidote or safening activity is not a theoretical determination but must be done empirically. Safening activity is determined empirically by observing the complex interaction of several biological and chemical factors, namely: the type of herbicide compound; the type of weed to be controlled; the type of crop to be protected from weed competition and herbicidal injury; and the antidote compound itself. Moreover, the herbicide and antidote must each possess chemical and physical properties enabling preparation of a stable formulation which is environmentally safe and easy to apply to the field.